Quality of video

ABSTRACT

The present invention is directed towards methods, devices and a signal format for providing information for achieving better perceived image quality of a transmitted video data stream. A video and information transmitting unit ( 28 ) in a device ( 20 ) transmits a video data stream and information about subjective quality relating to the video data stream in a signal comprising at least one frame with a header section, a motion vector section and a compressed image section. A device for processing a video data stream ( 32 ) includes a video and information receiving unit ( 34 ) which receives the signal, a decoding unit ( 38 ), which decodes the video data stream, and a control unit ( 36 ), which controls use of the information about subjective quality when processing the video data stream in order to achieve better perceived image quality.

TECHNICAL FIELD

The present invention relates to achieving better perceived imagequality of a transmitted video data stream.

BACKGROUND OF THE INVENTION

Video data streams, normally provided in the form of compressed imagesand motion vectors could possibly be decoded in different ways. Whenstreamed video is presented though, non-program content characteristics,such as frame rate, resolution and quantisation depth have differentimportance depending on the perceived subjective quality. However thisis not taken into account in the video decoders of today.

It is known to provide complexity parameters in graphical 3-Dapplications. This information can be used to reduce the quality of thedecoding if the complexity is high. This is done in order for a decoderto be able to produce a 3-D picture within an available time when thepicture is complex.

U.S. Pat. No. 5,027,206 describes a film mode signaling bit included ina bit stream. Such an inclusion does however not indicate anything elsethan that it is a film and not information about subjective quality ofthe film, for instance what type of film it is. The result is that thiscannot be used for optimal decoding, since films can be so called actionmovies with a lot of motion as well as dramas or wildlife movies, withless motion.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide better perceivedimage quality of a transmitted video stream in relation to limiteddecoding capabilities of a decoder and/or a post processor. To this endthe invention provides methods, devices, a signal format and a storagemedium as defined in the independent claims. Advantageous embodimentsare defined in the dependent claims.

For different elements in video streams like frames, groups of frames orscenes there are different requirements of non-program contentcharacteristics on the environment in which the video content ispresented. For instance the color is more important in video streamsshowing wildlife content, whereas the information regarding motion ofobjects are more important if the video stream is an action film. Todaythese different aspects are not taken into account when processing avideo stream, which leads to the video decoders and post processors oftoday not being used optimally. There is also a limited processingcapability in the video decoders of today, which means that a compromisehas to be made with respect to the different non-program contentcharacteristics when decoding a video data stream to be presented to anend user.

The present invention achieves the object by providing better knowledgeof the different contexts in which objects are shown in a video datastream for better use of the different decoding capabilities in a videodecoder.

According to one aspect of the invention, this is achieved by a methodof providing information for achieving better perceived image quality ofa transmitted video data stream, including the steps of: transmitting acoded video data stream to a receiving device and transmittinginformation about subjective quality relating to the video data streamto the receiving device in order for the receiving device to be able touse said information when processing the video data stream.

According to this aspect, the problem is also solved by a device forproviding information for achieving better perceived image quality of atransmitted video data stream, comprising: a video transmitting unit fortransmitting a video data stream to a receiving device, and aninformation transmitting unit for transmitting information aboutsubjective quality relating to the video data stream to the receivingdevice, in order for the receiving device to be able to use theinformation about subjective quality when processing the video datastream.

According to another aspect of this invention, this problem is alsosolved by a method of processing a video data stream comprising thesteps of: receiving a video data stream, receiving information aboutsubjective quality relating to the video data stream, and using theinformation about subjective quality when processing the video datastream in order to achieve better perceived image quality.

According to this aspect the problem is also solved by a device forprocessing a video data stream comprising: a video receiving unit forreceiving a video data stream, an information receiving unit forreceiving information about subjective quality relating to the videodata stream, a decoding unit for decoding the video data stream, and acontrol unit for controlling use of the information about subjectivequality when processing the video data stream in order to achieve betterperceived image quality.

According to yet a further aspect of the present invention this problemis furthermore solved by a signal format for use in transmitting a videodata stream comprising at least one frame with: a header section, amotion vector section and a compressed image section, wherein at leastone of the sections include information about subjective qualityrelating to the video data stream for enabling a receiving device to usethe information about subjective quality when processing the video datastream.

Preferred variations of the first mentioned aspects provide furtheradvantages by providing the information about subjective quality in thevideo data stream.

According to yet a preferred variation of the different aspect of theinvention, the information about subjective quality enablesprioritization of non-content program characteristics in a decoder.

According to one variation of the present invention, the informationabout subjective quality also enables better use of a post processor.

With the expression subjective quality is meant such things as an actionfilm or scene or a frame or group of frames of such a scene. It is thusrelated to such things like how much motion, color or perhaps detailthere is in a video sequence or a whole video data stream. With programcontent is meant the objects, like things or persons actually shown in avideo data stream. Subjective quality is thus related to the context inwhich objects in a video data stream are provided.

The term comprising is in no way to be interpreted limiting, but is tobe understood to be equivalent to the term including.

PCT-application EP01/11565 filed Apr. 10, 2001 discloses quality tagsthat are added to a bit stream. These tags indicate the quality of animage related to the position in a bit stream. One quality measurementioned is distortion. This is quite different than the subjectivequality according to the present invention.

The basic idea of the present invention is thus to provide informationabout subjective quality, which provides a decoder with the necessarytools needed for prioritizing between different non-program contentcharacteristics when decoding.

Additional benefits of the invention will be evident from the followingdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference madeto the enclosed drawings, where:

FIG. 1 shows a video data stream including subjective quality of videoparameters signaling according to an embodiment of the invention.

FIG. 2 shows a block schematic of an apparatus for sending informationabout subjective quality of video to a receiving unit and said receivingunit for receiving subjective quality of video information.

FIG. 3 shows a flow chart of a method of sending subjective quality ofvideo parameters.

FIG. 4 shows a flow chart of a method of receiving subjective quality ofvideo parameter.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 is shown a video signal 10 according to the present invention.The video signal can be a video signal according to any known standardsuch as MPEG-2, MPEG-4 or even more applicable an MPEG-21 signal. Thevideo signal 10 includes a frame of video data comprising a compressedimage section 12, a motion vectors section 14 and a header section 16.In the header section 16 there is included subjective quality of videoparameters 18 according to the invention. This information can be putinto each frame, into one frame of a group of frames or at the beginningof a scene including a number of group of frames. The information isalso to be seen as an indication of type of program content, like forinstance if a certain scene is having much motion or is slow in nature.The amount of information put into such a stream is actually dependenton the amount of work wanted to be put in by a video stream producer.FIG. 1 only shows a first frame of a video data stream. The streamnormally includes a number of frames, grouped into groups of frames,where subjective quality of video parameters are valid until they arerenewed at a frame, group of frame or scene level.

FIG. 2 shows a block schematic of a video coder or a device 20 forproviding information for achieving better perceived image quality,which video coder is connected to a device 32 for processing a videodata stream or a receiving device via a physical channel 30. Thephysical channel 30 can be any type of channel like for instance copperwire, optical or wireless. The video coder 20 includes a source encoder22, which source encoder codes a video data stream. The coder 20 alsoincludes a subjective parameter memory 24. Both the source encoder 22and the subjective parameter memory 24 are connected to a multiplexer26, which multiplexes subjective parameters 18 into the header of aframe in a source coded compressed video data stream. The multiplexer 26is connected to a video and information transmitting unit or sender 28,which might include formatting or potential channel coding. The sender28 is in turn connected to the physical channel 30. The physical channelis connected to a video and information receiving unit or subjectiveparameter extractor 34 of the receiving device 32. The subjectiveparameter extractor 34 is connected to a decoding unit or source decoder38. A control unit 36 is connected to the parameter extractor 34 and tothe source encoder 38. Finally a post processor 40 is connected to thesource decoder 38. The control unit 36 is also connected to the postprocessor 40.

Now a preferred embodiment of the present invention will be described inrelation to FIGS. 1 and 2. A first frame of a first group of frames of avideo data stream is generated in the source encoder 22. This streamdoes not yet have subjective quality of video parameters. For this firstframe the subjective parameter memory 24 submits two values, one firstfor indicating what type of movement will be present in the next groupof frames and one second for indicating what the importance of colorwill be in the next group of frames. These two values are set so thatthey have different importance, i.e. one value can be more importantthan the other value. Once the parameters have been inserted into theframe, the frame will be transferred to sender 28 for sending as signal10 to the receiving device 32 via the physical channel 30. Theparameters indicate a subjective quality of the next number of frames ofthe video data stream. New parameters are thereafter inserted for thenext group of frames etc. This continues for the whole video datastream.

The receiving device 32 receives the frame in the form of signal 10.When the receiving device 32 receives the frame it first demultiplexesand extracts the parameters from the video data stream in the subjectiveparameter extractor 34. The extracted parameters are forwarded tocontrol unit 36, while the rest of the video data stream is forwarded tosource decoder 38. The control unit 36 generates a first and secondcontrol signal in dependence of the received first and second parametersand makes the source decoder to set non-program content characteristicsaccording to these control signals when decoding the video data stream.The first control signal, which has been set in dependence on the firstparameter, sets the frame rate to be used when decoding, while thesecond parameter sets the color depth. These parameters are examples ofpreferred parameters at this point in time. It is possible to use moreclever and complex parameters instead. The control unit 36 also uses aprioritization scheme between the two parameters, in that one is moreimportant than the other. This also means that if the first parameterhas indicated that the program includes a big amount of movement and thesecond parameter has indicated a lower importance of color, the controlunit controls the source decoder 38 to have a high frame rate whileusing fewer bits than what is normally used for resolution. Afterdecoding the first frame of the video data stream, the source decoder 38forwards the decoded video data to post processor 40, which does somepost-processing of the decoded video data stream. Here the control unit36 influences settings or performance in the post processor 40 based onthe received parameters in order to achieve optimal perceived imagequality. In the preferred embodiment the motion compensation isinfluenced. However, it is also possible to influence such things asnoise reduction, frame/field up-conversion and the like. The decodercontinues decoding the following frames in the first group of framesusing the same prioritization scheme until a next first frame of afollowing group of frames is received, and then the above describedextraction and prioritization is repeated. This continues in the waydescribed above until the whole data stream has been decoded.

Now a method of providing information for achieving better image qualityaccording to the present invention will be described with reference toFIG. 3, which shows a flow chart of the method according to theinvention. First a video data stream is generated, step 42. Thereafterinformation about subjective quality concerning the data stream, in theform of a first and a second parameter, is inserted in the stream, step44. After this step the video data stream is transmitted to thereceiving unit, step 46, so that prioritization of non-program contentcharacteristics can take place, when decoding the stream. Theabove-mentioned steps are then repeated for the first frame of allfollowing groups of frames of the video data stream.

Now a method of processing a video data stream will be described withreference to FIG. 5, which shows a flow chart of said method. First avideo data stream is received, step 48. Thereafter information aboutsubjective quality in the form of the first and second parameter isextracted from a first frame of a first group of frames in the stream,step 50. After this the decoding of the rest of the data in the firstgroup of frames is being performed, where the non program-contentcharacteristics of the decoding have been prioritized according to thereceived information, step 52. This means that non-program contentcharacteristics receive different attention because of theprioritization. The quantisation depth and resolution could for instancebe lowered in overload situations while the frame rate could be kept upto the desired level as a result. This also means that the subjectivequality information is used when decoding the video data stream.Thereafter the post processing is also controlled according to thereceived information about subjective quality, step 54. Theabove-mentioned steps are thereafter repeated for each group of frames.

With the described preferred embodiment of the invention there has beendescribed a way to better decode a video data stream in an environmentof limited resources. According to the present invention informationabout subjective quality of video is transferred to a decoder, whichuses this subjective information in prioritizing non-program contentcharacteristics when decoding. Such characteristics are for instanceframe rate, resolution and quantisation depth, which can be prioritizedso that the video data stream is decoded with different levels ofrefinery for these characteristics. One characteristic then gets higherattention than another characteristic for a frame, group of frames orscene. In this way frames having a lot of motion information can forinstance be indicated as such, so that the non-program characteristicsimportant for motion like frame rate can get a higher priority, whileframes having lower content of motion can get a prioritization ofresolution and quantisation depth so that for instance colors get ahigher resolution. With the preferred embodiment of the presentinvention different parts of a video data stream can have the parametersset differently, which makes it possible to decode the video data streamwith a good perceived quality for the viewer, even when the differenttype of scenes are shown in the same stream.

The invention can be varied in many ways. First of all there wasdescribed providing two parameters. The invention is not limited to twoparameters, but one or more than two can be provided. There does alsonot need to be a 1:1 correspondence between a parameter and anon-content characteristic. A parameter can for instance be used todetermine the priority of all or some of the non-contentcharacteristics. Furthermore, frame rate, resolution and quantisationdepth are just a few of the possible non-program contentcharacteristics, which can be prioritized according to the invention.There are thus a number of parameters that can control the performanceof scalable decoders.

According to the present invention control of some characteristics inthe post-processing based on the subjective quality of video parametersis also performed. This was described as being done in addition tocontrol of the decoding. This control could however also be done insteadof the control of non-program content characteristics of the videodecoder. Another variation of the present invention is that subjectivequality of video parameters do not have to be provided once for eachgroup of frames or in the first frame of a group of frames. They canequally as well be provided in any of the frames of a group of frames,in each frame, each scene or just once for the whole video data stream.In case they are just provided once for the whole stream, theprioritization is done once for the whole video data stream. In thiscase there is no adjustment for different scenes, frames or group offrames of the video data stream, but the same prioritization applies forthe whole video data stream. In this special case, the information doesalso not have to be provided in the actual video data stream but can bereceived from for example an electronic program guide. It is furthermorepossible to provide the subjective quality of video parameters in aseparate information stream or separate information signal, even if ascene, frame or group of frames is to be controlled using thisinformation. However if decoding control is to be varied duringdecoding, the video data stream has to be synchronized with the signalcomprising subjective quality of video parameters. In this case thevideo data stream and the information stream can be receivedsimultaneously. As an alternative the subjective quality of videoparameters can be received or downloaded beforehand and not necessarilyfrom the same source as the video data stream. The control unit thenneeds to synchronize between both information sources in order to applydifferent decoding of the video stream according to the downloaded orreceived (through a secondary stream) parameters.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. In the claims, any reference signsplaced between parentheses shall not be construed as limiting the claim.The word ‘comprising’ does not exclude the presence of other elements orsteps than those listed in a claim. The invention can be implemented bymeans of hardware comprising several distinct elements, and by means ofa suitably programmed computer. In a device claim enumerating severalmeans, several of these means can be embodied by one and the same itemof hardware. The mere fact that certain measures are recited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage.

1. Method of providing information for achieving better perceived imagequality of a transmitted video data stream, including the steps of:transmitting a coded video data stream to a receiving device, andtransmitting information about subjective quality relating to the videodata stream to the receiving device in order for the receiving device tobe able to use said information when processing the video data stream.2. Method according to claim 1, further comprising the step of insertingthe information about subjective quality in the data stream forindicating the importance of processing non-program contentcharacteristics in view of content quality, so that the informationabout subjective quality can be extracted from the video data stream. 3.Method according to claim 1, wherein the information about subjectivequality includes program information from an electronic program guide.4. Method according to claim 1, wherein the information about subjectivequality includes information about content type per frame, per group offrames or per scene.
 5. Method according to claim 1, wherein theinformation about subjective quality includes information enablingprioritization of non-content program characteristics in the receivingdevice.
 6. Method of processing a video data stream comprising the stepsof: receiving a video data stream, receiving information aboutsubjective quality relating to the video data stream, and using theinformation about subjective quality when processing the video datastream in order to achieve better perceived image quality.
 7. Methodaccording to claim 6, wherein the step of using includes using theinformation about subjective quality for control of non-program contentcharacteristics when decoding the video data stream.
 8. Method accordingto claim 6, wherein the step of using includes using the informationabout subjective quality for post processing of the video data streamafter decoding.
 9. Method according to claim 6, wherein the informationabout subjective quality is included in the video data stream forindicating the importance of processing on non-program contentcharacteristics in view of content quality and further including thestep of extracting the information about subjective quality from thecoded video data stream.
 10. Method according to claim 6, wherein theinformation about subjective quality includes program information froman electronic program guide.
 11. Method according to claim 9, whereinthe information about subjective quality includes information of contenttype per frame, per group of frames or per scene.
 12. Method accordingto claim 7, wherein the non-program content characteristics are any ofthe characteristics frame rate, resolution, color depth or motionestimation.
 13. Method according to claim 7, wherein the step of usingincludes prioritizing the different non-program content characteristicsbased on the information on subjective quality and controlling thedecoding of the video data stream according to the prioritization made.14. A device for providing information for achieving better perceivedimage quality of a transmitted video data stream, comprising: a videotransmitting unit for transmitting a video data stream to a receivingdevice, and an information transmitting unit for transmittinginformation about subjective quality relating to the video data streamto the receiving device, in order for the receiving device to be able touse the information about subjective quality when processing the videodata stream.
 15. Device according to claim 14, wherein the videotransmitting unit and the information transmitting unit are incorporatedin the same transmitting unit, so that the information about subjectivequality is included in the video data stream for indicating theimportance of processing on given non-program content characteristics inview of content quality.
 16. Device according to claim 14, wherein theinformation about subjective quality includes information enablingprioritization of non-content program characteristics in the receivingdevice.
 17. Device for processing a video data stream comprising: avideo receiving unit for receiving a video data stream, an informationreceiving unit for receiving information about subjective qualityrelating to the video data stream, a decoding unit for decoding thevideo data stream, and a control unit for controlling use of theinformation about subjective quality when processing the video datastream in order to achieve better perceived image quality.
 18. Deviceaccording to claim 17, wherein the control unit is arranged to use theinformation about subjective quality for control of non-program contentcharacteristics when decoding the video data stream.
 19. Deviceaccording to claim 17, wherein information about subjective quality isincluded in the video data stream, the video and information receivingunits are incorporated in the same receiving unit and the control unitis arranged to extract the information about subjective quality relatingto the video data stream from the video data stream.
 20. Deviceaccording to claim 17, wherein the control unit is further arranged toprioritize the different non-program content characteristics based onthe information on subjective quality and to control the decoding of thevideo data stream according to the prioritization made.
 21. Deviceaccording to claim 17, further including a post processor for postprocessing of the decoded video data stream, wherein the control unit isarranged to use the information about subjective quality for control ofthe post processor.
 22. A signal format for use in transmitting a videodata stream comprising at least one frame with: a header section, amotion vector section and a compressed image section, wherein at leastone of the sections include information about subjective qualityrelating to the video data stream for enabling a receiving device to usethe information about subjective quality when processing the video datastream.
 23. Signal format according to claim 21, wherein the informationabout subjective quality includes information enabling prioritization ofnon-content program characteristics in the receiving device. 24.(currently amended) A storage medium on which a signal format as claimedin claim 22 has been stored.